A cystic hygroma (or haemangiolymphoma) is a benign congenital proliferation of lymphoid tissue. It is well recognized in pediatric practice but seldom presents in adulthood.

Hygromas are probably the result of sequestration of fetal lymphatic tissue that has retained its potential for growth. Three types are described: (1) capillary - characterized by small, thin-walled lymphatic channels, (2) cavernous - large channels with a fibrous coat; and (3) cystic - characterized by large cystic endothelial-lined spaces.

The treatment of choice is surgical excision but this can be technically demanding, especially if there is deep extension. Recurrence can occur if the lesion is not fully excised.

On imaging the major differential diagnosis is hemangioma.